


Rubedo Remiges

by Jason_M_Lee



Category: Fullmetal Alchemist - All Media Types, Fullmetal Alchemist: Brotherhood & Manga, Kingdom Hearts
Genre: Alternate Universe - Canon Divergence, Crossover, Crossovers & Fandom Fusions, F/M, Forehead Touching, Gen, Light Angst, Originally Posted on FanFiction.Net, Romantic Friendship
Language: English
Status: Completed
Published: 2018-09-15
Updated: 2018-09-15
Packaged: 2019-07-12 18:52:31
Rating: General Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,096
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16001225
Author URL: https://archiveofourown.org/users/Jason_M_Lee/pseuds/Jason_M_Lee
Summary: The assumption that darkness and light cannot be truly understood is true. The assumption that it can't be incorporated with alchemy is false.





	Rubedo Remiges

**Author's Note:**

> _Fullmetal Alchemist_ © Hiromu Arakawa and Square-Enix. _Kingdom Hearts_ © Disney and Square-Enix

It used to be normal.

The day started out normal. Hawkeye's usual cup of coffee on his desk (two sugars, a splash of cream, and a hint of cocoa) was normal. Havoc struggling to get over his most recent break-up, Fuery repairing the field radios, Falman and Breda going through paperwork was also normal. Even Edward - Major Elric of the Department of Alchemical Abuse and Exploitation - slamming down the latest stack of reworked files was normal.

Except that both Edward and Roy had immediately felt what seemed like a very strong chill down their backs. The former alchemist, having just reached the doorknob to return to his office, glanced back at his commanding officer with wide eyes. The older man stared back, recognizing the feeling of something absolutely _wrong_.

"General?" Hawkeye spoke, noticing the two men's actions and drawing the attention of the rest. "Major?"

"Did..." Ed swallowed thickly, turning away from the door. "Did any of you guys just feel that?"

Five heads shook after a moment's pause. Before Fuery could ask what the younger blonde meant by that, screams and yells outside caught their attention, prompting them to move and be greeted by what could be tantamount to pandemonium.

Black creatures with chilling yellow eye were swarming throughout the hall, claws leaving behind scratches on any person they were latched onto. Some were simple and small, many others had a black and red crest somewhere on their bodies. What was even more terrifying was seeing a helmeted one plunge its claw into an unlucky sergeant's chest and yanking out what they could only call a pink glowing heart before crushing it. To their horror, the fallen sergeant slowly got back up, eyes blank and yellow as well having tendrils of shadow that reminded the alchemists far too much of the hands of Pride and from the Gate latching onto her. Turning to them, she blinked only once before leaping at them with an inhuman screech.

It was all but instinct that had Riza shooting the poor woman right in the middle of the forehead, giving her a swift end of a painful misery. At the sound, the rest reacted.

"Falman, Havoc! Find any other survivors and see if you can coordinate them into confining the creatures!" Roy barked, now having yanked his gloves on and soon striking every creature he could aim at without burning any other military staff. Riza's shots on the intruders had little affect if she aimed anywhere else other than between their eyes, but his flames made some breathing room. "If not, see if we can get the MPs in the city to watch out for the civilians! Breda, Fuery! Contact Central and warn them that they and the other headquarters may be also under attack! See if you can also contact any other people associated with us!"

"Mustang-"

A clap and a transmuted spear was quickly thrust into Edward's hands, who had to hastily reholster his gun.

"Hawkeye, Elric! You two are with me while we try to find where they're coming from!" Mustang immediately took off, setting more of the creatures on fire. "MOVE!"

Darkness soon took over the blue sky.

* * *

_Blackness, blackness, blackness everywhere._

_It gripped him, his entire being, all of his senses._

_It was worse than the aftermath of Ishval._

_It was worse than finding out Hughes' death._

_He felt that he was practically teetering on that very thin line again, when he had confronted and all but completely stomped over Envy down in the tunnels._

_That was all it took for the Heartless to try and make him another target._

_Feeling the biting chill seizing his chest, it felt worst than when he was forced to do human transmutation by Pride. Worst than when he was dismantled, molecule by molecule, and then unceremoniously reassembled in a dump, blind, in front of Father._

_Useless._

_All that work, and everything of his world, disappearing..._

**"You do not belong here, alchemist. Nor do you belong there."**

_A familiar voice, but it felt as if the speaker lacked the usual unsettling grin._

_The speaker was solemn, honest._

_Truthful._

**"You humans often speak of finding the light within the darkness."**

_He was fighting now, remembering everything, but not knowing how long time had passed._

_The chill was so tempting, feeling as the blackness seeped into him. It would be easy to slip into the darkness, to ignore the pain that was all but slowly consuming him._

_So easy._

_When has the path he had chosen to walk on ever been that easy?_

_Never._

**"If that's the case, then find your light."**

_One hand finally broke free from the creeping mass, just as the pain in his chest reached a crescendo._

'Riza...'

_A pause that seemed to hint at a genuine smile._

**"...Alchemist of Flames."**

_A snap._

* * *

"How is he?"

Aerith looked up from mending a blue jacket to see her boyfriend peeking through the door. "The only improvement is that his fever's broken."

Zack nodded as he stepped in with a tray. "That's good. But, I'm still a little worried, especially the uniform he had on."

"Do you think he came from a world where he was part of a military?"

He fingered the decorations on the shoulder after setting down the food on the table, frowning. "From the bar, he's definitely high ranking." Moving over, the swordsman studied the comatose man, taking note of the scars on the hands. "If anything, I'd say that he's been steeped in a good amount of darkness, and not just the literal kind. The way we found him..." A sigh from the normally cheerful man. "He's lucky."

She had to agree. Several of Radiant Garden's construction workers and Leon had practically stumbled upon the dark-haired man near the ramparts a week ago, a small group of Shadows surrounding him. While covered in a variety of lacerations and no doubt suffering from some form of head trauma, the man had been stubbornly keeping his attackers at bay by constantly snapping his fingers on both hands, which seemed to create flames. But Leon had noticed that the fire was weakening with each snap while the wielder struggled to defend himself. It was only when the man finally passed out that Leon took care of the Heartless, ordering the workers to get the newest victim to the hospital. Ever since then, the Committee had been taking turns keeping watch over the sleeping man.

"What else can you tell, Zack?"

"These gloves..." He pulled off his own and carefully felt the white ones, noticing the scratchy texture as well the red circle design on the back. "He was wearing these when they found him, right?"

Aerith nodded. "Nataro said that whenever he snapped his fingers, fire burst out from his fingertips, almost like a flamethrower."

Zack made a thoughtful sound. "Something unique to his world then. Welp, the only thing left is for Mr. Sunshine here to wake up." He dropped a kiss to her forehead. "And I gotta head back to patrol."

The flower girl smiled when he lingered, leaning in just a little bit. "You know Cid's claymores mean that you don't have to go on patrol."

"True, but it'll help keep me limber until the next shift for the construction yards." A cheeky salute before sauntering off. "Don't forget to holler if you need help."

* * *

He found him at the ramparts, looking out at the derelict castle and the teeming mass of Heartless below.

"How is it possible..." Roy spoke first, voice wavering and in disbelief.

Cloud couldn't blame the man. To a person who was at heart a scientist as well a soldier, learning that something unquantifiable like darkness and light could have actual physical effects on people - beyond psychological - had come as a shock. Compounding that was his own trip through the darkness after his world was lost to it. It had taken quite some time for the recovering Flame Alchemist to fully grasp the concepts that was almost second-nature to the Restoration Committee.

"Sometimes, there are a lot of things that just can't be quantified," Cloud answered just as quiet. Most would've found him a bit out of character, Yuffie especially. Leon, Aerith, Zack, and Tifa - and maybe the two Keyblade wielders - were probably the only ones to understand the reason for his gentleness. "Like a person's heart, and the ability to whether withstand, be consumed, or control their inner darkness and light."

Silence from the black-haired man, head dropping a bit as if deep in thought. "...a person's soul," he mumbled, as if recalling something.

Cloud frowned in puzzlement at that comment but nodded. "For us that have encountered both, it's at best a form of power and a necessary part of existence. Sometimes..." His left shoulder blade ached, but only briefly. "The darkness feels easy to control, but in reality..."

"...it can turn on you without warning," the older man finished hoarsely. Roy understood. He had seen what obsession with or related to alchemy could result in.

Finally noticing how white-knuckled Roy was clutching his shoulders, Cloud gave a soft sigh. "The way you're fighting, restraining your inner darkness isn't going to help."

"Then how do I deal with it?" Finally, a wince of pain flashed through.

Considering how long the man had been stuck in the darkness and what he had grown up with, the swordsman couldn't help but feel sorry for Roy. "How do you control the alchemy on your world?"

"Circles is the basis of every alchemical transmutation, as they are the conduit for the necessary energy. The shapes represent the elements that are to be used for transmuting the materials that we're working with. As nothing can be gained without sacrificing something of equal value," Roy practically recited.

"Then work with that." Hesitation, and then a rough pat on the shoulder before leaving. "Just remember: your inner darkness is yours and forever only yours to truly control."

* * *

It wasn't the usual alarm that had him running with Leon outside to deal with the new onslaught of Heartless that had popped up in the Great Maw during a rare rainstorm. (Let the others call him "General Useless" again! He has clap alchemy now!)

It wasn't the habit of slipping on gloves and incinerating every yellow-eyed creature in sight while fighting against the hypnotizing call of the darkness within himself.

It also wasn't keeping an eye out for civilians that scrambled to safety, occasionally using clap alchemy to create additional defenses just in case. (Merlin had been utterly fascinated by the differences of what he knew and what Roy had been taught, and gladly helped the Flame Alchemist better refine his control. Even if it tended to result in singed clothing and scorched furniture.)

Nor was it hearing the oh-so familiar war cry of **"BEHOLD THE GRACEFUL AND GLORIOUS ALCHEMICAL ARTS THAT'S BEEN PASSED DOWN THE ARMSTRONG LINE FOR GENERATIONS!"**

Or the very curt "Quit prattling and just take them down, Alex!"

Well, the previous two gave him hope that he immediately shelved aside to focus roasting a Wyvern that tried to dive bomb Yuffie.

No, it was finally seeing his beloved Lieutenant - wait, she was promoted to major - Riza Hawkeye completely surrounded by Hammer Frames, Morning Stars, Armored Knights, and Surveillance Robots. The sight of her taking out Heartless after Heartless with her usual calm precision was something so profound that it made Roy Mustang hesitate briefly. He hadn't given up hope ever since arriving in Radiant Garden. Rather, he kept the belief that he'll one day see some of those he knew alive - and whole, preferably whole since he didn't want to handle another Fullmetal - in his mind during the days of recovery and weeks of helping out the Restoration Committee.

The sight of an Arch Behemoth aiming towards her had his blood running cold.

"HAWKEYE!"

Red-brown eyes noticed him and when she saw him snapping his right hand above him while his left took out those in front of him, Riza turned and nearly froze at the looming horned Heartless before she immediately ran towards him.

_Blood pouring from her neck..._

_Her life in his hands back then..._

Neither were going to make it with all the smaller Heartless in front of them.

The darkness tempted again.

_Those mocking words..._

_Slim luck, sheer luck._

Desperation and a clap that, to his ears, seemed louder than ever before.

_But... Mei Chang isn't here._

_No alkahestry here._

This time, the circle in his mind reconstructed the siren call.

_Her life in his hands..._

_...once again._

To those that observing from a distance, it was as if an enormous bomb had been set off.

For the Armstrongs that were familiar with the Flame Alchemist, they were surprised at how much brighter and hotter the fires were in the unexpected explosion, nearly a blinding yellow. Leon, Tifa, and Yuffie were taken aback at how the roaring flames formed walls around them, incinerating every Heartless so fiercely and quick that the smaller ones barely had time to react. The larger ones flailed in pain before disintegrating into the ether.

When the inferno gradually lessened to more bearable levels of heat, the others were able to pick their way through stray fires to where Roy and Riza were last seen and what met their eyes had them staring.

Protruding out of Roy's right shoulder blade was an enormous wing that was on fire, shifting from dazzling whitish-blue to brilliant yellow and finally bright red on the tips of the flight feathers, and it burned cheerfully despite the heavy downpour. From what Leon and Olivier could tell, the wing seemed to form a protective barrier around the pair before it pulled back to reveal a wide-eyed Riza staring at an exhausted looking Flame Alchemist. Even with the flickering flames, neither shirt or hair on Roy showed any signs of burning, other than a ripped hole from where the wing had sprouted out through.

"General..."

A weak smile before the flaming wing dissipated into small sparks and he all but fainted on top of a startled sniper. The last thing to reach his ears was Riza frantically calling his name.

* * *

Fingers gently brushing his bangs was what Roy awoke to. Blinking to clear up the blurry image, he was relieved to see Riza. Her snatching her hand away almost guiltily was a nice bonus.

"Sir-"

"You're here."

Her face betrayed nothing, but he could see relief in her eyes.

"You're here, too. Sir."

Trying to sit up resulted a hiss of pain, and her gently pushing him back down onto the bed. Once again, the familiar hospital walls greeted him and to his surprise, it was the same one that had been assigned to him when he had first arrived to Radiant Garden.

"The Armstrongs?"

"General Armstrong is discussing everything over with Mr. Leon." Her slight pause at "discussing" hinted at more of a interrogation, and Roy tried not to chuckle. Everything they had learned in their world was going to be tossed and shaken on its head. Magic, at first glance, seemed to go against everything that was taught from the perspective of alchemy. Yet Merlin had been quick to correct that magic in any of the other worlds still required concentration and practice, and those that didn't had enough power within themselves can never cast spells. Of course, Olivier would immediately see how to utilize magic as a weapon. "Major Armstrong has volunteered with the reconstruction efforts, although I believe that some of the workers were less than happy with some of the additions he had placed in."

A nod, finally accepting her help to sitting up in order to drink water. "Did anyone else arrive?"

"The rest of our team has been integrating themselves with the Committee quite smoothly. Havoc has joined up Mr. Cid and Mr. McDuck on how to obtain supplies from other worlds much quickly or make our own here more efficiently. Breda and Fuery have taken upon themselves to familiarize themselves with Tron." A faint hint of disbelief in her voice on mentioning the computer AI. "Falman has taken to the fort's and Merlin's libraries. Regarding the Elrics, they have made it safely as well, alongside Their Highnesses Ling Yao and Mei Chang, plus Lan Fan. They're all recovering quite well, although I believe that Edward and Ling will require some assistance of being removed from the cafeteria multiple times."

Roy furrowed his brows. "What of the Rockbells?"

Riza paused, eyes softening. "The most recent I saw of Miss Winry, Miss Aerith was consoling her. Pinako Rockbell... did not make it with us."

A bout of grief, mingling with the happiness that at least this many people of his world had made it here alive. Roy knew he'd be asking too much.

"Sir... Roy." She hesitated. She rarely hesitated. "There's been some questions."

It was rather inevitable. Of course, the single flying appendage of flame that didn't burn either of them, not naturally a part of the human body, and still continued to burn even in the heavy downpour. He knew Edward was going to have difficulty accepting the existence of magic as well actual affects of dark and light on humans (Roy himself had trouble at the beginning), but with this new development, the former alchemist was going to be on a rampage on trying to find the logic of how things worked here. The back of his right shoulder throbbed briefly, as if reminding him.

Perhaps he should introduce Fullmetal to Sora? The young Keyblade wielder may not have been the most best at explaining metaphysical concepts such as magic (that was more of Merlin and the Fairy Godmother's department), but regarding darkness and light, he had a natural knack of making other understand just a little more easily. It was also Sora that taught Roy to occasionally think with his heart and not just solely with the scientific or soldier aspect of his persona. Edward wasn't the only person to defy logical thinking, but he rarely saw it from the perspective of others, so maybe Sora could show a bit of light on that. Besides, the younger alchemist always did like learning something new, even if he was proven wrong.

A small smile crept onto Roy's face.

"The only answer that I can give right now..."

Fingers interlaced with familiar calluses from long usage of firearms.

"...is that my inner darkness has finally regained its light."

Riza blinked once, then simply rested her forehead against his as she tightened her fingers.

**Author's Note:**

> Written for LJ community FMA Fanfic Contest prompt 106 "Crossovers" back in 2011.
> 
> Yes, somewhat AU regarding Zack from _Birth By Sleep_. But I'm a bit of a Zack/Aerith diehard.
> 
> "Rubedo" may sound familiar to those that have played the _Xenosaga_ series, but it's used in relation to historical alchemy. Latin for "redness", and the final stage of the "alchemical opus" after nigredo, albedo, and citrinitas, in that order.
> 
> Remiges are the flight feathers found on bird wings.


End file.
